Liquid crystal display devices display images taking advantage of the optical and electrical properties of liquid crystal materials. Liquid crystal display devices have many advantages, such as light weight, low power consumption, and low driving voltage, in comparison with CRTs, plasma display panels, etc. A liquid crystal display device includes a liquid crystal layer interposed between glass substrates. Light generated from a light source passes through the liquid crystal layer where the light transmittance is controlled. The light having passed through the liquid crystal passes through a color filter layer. The liquid crystal display device uses the light having passed through the color filter layer to realize full-color images on a screen based on additive color mixing.
Dyeing, printing, electrodeposition, and pigment dispersion are generally known as methods of producing color filters for liquid crystal display devices. Dyeing methods have been explored in the past. However, dyeing methods are difficult to apply to the production of color filters because dyes are inferior in resistance to external factors, including heat, light, and chemicals, to pigments. Dyeing methods involve complicated processing steps, thus lacking economic efficiency. In view of these disadvantages, pigment dispersion is generally applied to the production of color filters at present. The lower transmittances of pigments than dyes have been overcome by advanced techniques for the micronization and dispersion of pigments. Color filters produced by pigment dispersion are stable against external factors, such as light, heat, and solvents, due to the use of pigments. Pigment dispersion facilitates the production of color filters for large-screen high-precision color displays by photolithographic patterning. For this reason, pigment dispersion is presently the most widely used method. Pigment dispersion using pigments requires a large number of additives to stabilize the state of the pigments and micronize the pigment powders. Further, pigment dispersion involves very laborious and troublesome processes.
As an alternative to pigment dispersion, the use of colorants as mixtures of pigments and dyes was considered to achieve improved physical properties. The colorants contributed to improvements of luminance and contrast to some extent, but the above-mentioned problems of the pigments were inevitable due to the addition of the dyes to the pigments, and as a result, the improved luminance and contrast were not as satisfactory as expected.
Under these circumstances, research aimed at the development of new dye compounds has recently been conducted to achieve high luminance, contrast, and resolution. Dyes can be used to produce color resists in a simpler manner than pigments while eliminating the problems of poor dispersibility and aggregation of pigments.
Particularly, numerous attempts have been made to use triarylmethane dyes, which are dye compounds under active development. The triarylmethane dyes are effective in achieving improved luminance and contrast due to their high transmittance at 420 to 450 nm but have low solubility in solvents used in coloring compositions for color filters and are poorly resistant to heat.